The present invention relates to mixtures of various adsorption materials whose adsorption properties supplement each other in the mixture.
Contact granules and adsorber granules, including those based on iron oxides and/or iron oxyhydroxides, have already been described. They are used predominantly in continuous processes, where they are usually found in tower- or column-like apparatuses, through which the medium to be treated flows, and on the external and internal surface of the granules of which the chemical or physical reaction or adsorption processes take place.
The flowing media exerts force on the granules, which can lead to abrasion and/or to movement including vigorous agitation of the granules. As a result, the granules collide with one another and in consequence unwanted abrasion results. This leads to loss of contact or adsorber material and to contamination of the medium to be treated.
Iron oxide and iron hydroxide-containing adsorption media/reaction media are advantageously usable, for example, in the field of water purification or gas purification. In water purification, this medium is used in filters or adsorber columns through which flow passes horizontally or vertically, or by addition to the water to be treated, for removing dissolved, suspended or emulsified organic or inorganic phosphorus compounds, arsenic compounds, antimony compounds, sulfur compounds, selenium compounds, tellurium compounds, beryllium compounds and cyano compounds and heavy metal compounds from. Examples thereof can be drinking water, service water, industrial, municipal wastewater, mineral water, holy water and therapeutic water and also garden pond water and agricultural water. It is also possible to use what are termed reactive walls for removing said pollutants from groundwater and leachate water-bearing formations from contaminated sites (landfills).
In gas purification, the medium is used in adsorbers for binding unwanted constituents, such as hydrogen sulphide, mercaptans and prussic acid, and other phosphorus compounds, arsenic compounds, antimony compounds, sulfur compounds, selenium compounds, tellurium compounds and also cyano compounds and heavy metal compounds in exhaust gases. It is also possible to adsorb gases such as HF, HCl, H2S, SOx NOx.
It is also possible to remove compounds of phosphorus, arsenic, antimony, selenium and tellurium, and also cyano compounds and heavy metal compounds from waste oils and other contaminated organic solvents.
Contact granules and adsorber granules based on iron oxides and/or iron oxyhydroxides are also used to catalyze chemical reactions in the gas phase or in the liquid phase.
Various processes are known to remove the trace substances and pollutants from aqueous systems using adsorption media. Thus DE-A 3 120 891 describes a process in which, to remove principally phosphates from surface water, filtration is performed through activated alumina having a particle size of 1 to 3 mm.
To remove pollutants from water, DE-A 3 800 873 describes an adsorption medium based on porous materials, for example hydrophobized chalk having fine to medium particle size.
DE-A 3 703 169 discloses a process for preparing a granulated filter substance for treating natural water. The adsorbent is prepared by granulating an aqueous suspension of kaolin with addition of pulverulent dolomite in a fluidized bed. The granules are then fired at 900 to 950° C.
DE-A 40 34 417 discloses a process for preparing and using highly reactive reagents for purifying exhaust gas and wastewater. Descriptions are given here of mixtures of Ca(OH)2 with additions of clays, stone flours, fly dust and fly ashes which can be prepared so as to be porous and have a surface area of approximately 200 m2/g.
DE-A 4 214 487 describes a process and a reactor for removing impurities from water. Flow of the water impurities passes horizontally through a funnel-shaped reactor in which the sorbent used for the water impurities is very finely divided iron hydroxide in flock form. A disadvantage of this process is the use of the flock-form iron hydroxide which, owing to the low differences in density between water and iron hydroxide leads to the fact that the reactor for removing the impurities can only be operated at very low flow velocities. Moreover, there is the risk that the sorbent, possibly already loaded with pollutants, is discharged from the reactor together with the water.
JP-A 55 132 633 describes a granulated red mud, a by-product of aluminum production, as adsorbent for arsenic. This is composed of Fe2O3, Al2O3 and SiO2. The stability of the granules and the granulation process are not reported therein.
DE-A 19 826 186 describes a process for preparing an iron hydroxide-containing adsorption medium. An aqueous polymer dispersion is mixed into iron hydroxide in water-dispersible form and then dried. As a result a material is obtained in which the iron hydroxide is firmly embedded in the polymer and is said to have a high binding capacity for the pollutants usually present in the wastewater or exhaust gases.
In the publications DE-A 10 047 997 equivalent to PCT/01/10926, DE-A 10 047 996 or PCT/01/10513 adsorber granules based on iron oxides or iron oxyhydroxides are described as having been successfully used, inter alia, for removing arsenic ions and other pollutants from drinking water.
DE-A 10 115 414 or PCT/01/10634 describes, for example, granules based on iron oxide and/or iron oxyhydroxides which comprise as binder Al oxides, Ti oxides and/or Mg oxides. DE-A 10 047 996 or PCT/01/10513 describe the iron oxide or iron oxyhydroxide embedded in an Fe(OH)3 matrix. As a result the granules have an extraordinarily high stability without impairing the arsenic adsorption.
DE-10 047 997 or PCT/01/10926 describes granules from finely particulate or nanoparticulate iron oxides or iron hydroxides having a high specific surface area which, in addition to a high adsorption capacity towards arsenic ions and heavy metal ions, have high strength and abrasion stability when they are used in a fixed bed.
DE-A 10 129 307 or PCT/01/10930 describes various adsorption vessels which can be packed with the above-mentioned granules, which can be used for removing pollutants in water treatment.
DE-A 4 320 003 describes a process for removing dissolved arsenic from ground-water using colloidal or granulated iron hydroxide. For the use of fine, suspended iron(III) hydroxide products, it is recommended here to introduce the iron hydroxide suspension into fixed-bed filters which are packed with granular material or other supports having a high external or internal porosity. This process is also attended by the disadvantage that, based on the adsorbent “substrate+iron hydroxide”, only low specific loading capacities are achievable. Furthermore, there is only weak binding between substrate and iron hydroxide, so that in a subsequent treatment with arsenic-containing water, there is the risk of discharge of iron hydroxide or iron arsenate. In this publication, the use of granulated iron hydroxide as adsorber material for a fixed-bed reactor, which is prepared by freeze-drying is additionally mentioned.
The use of granules, which can be produced by compacting, for example, pulverulent iron oxide, by using high linear forces, has already been mentioned. Such granules have been described for homogeneously coloring liquid concrete. The use of high linear forces in compacting is greatly energy intensive and costly and the stability of the compacted material is unsatisfactory for relatively long use in adsorbers. Therefore, such materials are only considered for use with limitations in adsorbers, in particular continuously operated adsorbers, for the purification of water. In particular, during servicing or cleaning the adsorber systems by backwashing (see below), such granules, as a result of the associated agitation of the same, lose large amounts of substance. The backwash water is made highly turbid due to the abrasion. This is unacceptable for several reasons: firstly, adsorber material is lost which, after a long service time, is highly loaded with impurities and is therefore a toxicological hazard. The wastewater stream is then polluted with the abrasion which can sediment and thus lead to impairment of the piping systems, and finally the sewage treatment plant is undesirably physically and toxicologically polluted, to name just a few reasons.
For water treatment, preferably, continuously operated adsorbers are used, which are frequently operated in groups arranged in parallel. At peak consumption times, the adsorbers present are then operated in parallel in order to prevent the flow velocity from increasing above the design-limit maximum. During times of lower water consumption, individual adsorbers, for example, the adsorber material being exposed to particular stresses, as are described in more detail below are taken out of operation and can then be serviced.
In water treatment, preferably continuously operated adsorbers are used which are frequently operated in groups arranged in parallel. To remove organic pollutants from water, such adsorbers are charged, for example, with activated carbon in granulated or pulverulent form.
Ion exchange resins or zeolites are used, inter alia, for water softening and for removing numerous cations and anions.
Activated alumina in various particle sizes is principally used for removing fluorides and arsenic compounds.
Frequently there is encountered the problem of having to remove a plurality of constituents of different types simultaneously from one and the same water source. Usually this is performed sequentially by a plurality of series-connected adsorption columns.
An object underlying the present invention was therefore to mix highly reactive reagents and compositions based on, in particular, dry, pulverulent or granulated mixtures of iron oxides, iron (oxy)hydroxides and other adsorption media/reaction media, with or without additives, for example binders, for purifying waters. The purifying water can be from the group of drinking water, service water, mineral water, garden pond water, agricultural water, holy water and therapeutic water and/or gases which contain pollutants. The reagents and compositions are distinguished by high purification performance and landfill safety of the products, and processes for their production and their use. The mixture of the adsorption media/reaction media should ensure a high combined binding capacity and as a result high removal of the pollutants present or dissolved in liquids and gases, but which, at the same time, should withstand the mechanical and hydraulic stresses in the adsorber housings or systems. In addition, for safety, and for the filtration performance of installed filters, it should prevent the discharge of suspended impurities or abraded adsorber parts which are possibly loaded with pollutants.
Filter cartridges for purifying liquids, preferably contaminated water, which can also contain an adsorption medium, are known in various embodiments. To remove solids from waters, membrane filter candles, for example, in suitable housings are used. The company Brita Wasser-Filter-Systeme GmbH has disclosed cartridges and apparatuses for treating liquids (DE-A 19 905 601; DE-A 19 915 829; DE-A 19 814 008, DE-A 19 615 102, DE-A 4 304 536, U.S. Pat. No. 6,099,728). These apparatuses are highly suitable for the complete or partial desalination of drinking water in domestic jugs immediately before use of the drinking water.
U.S. Pat. No. 4,064,876 discloses a filtration unit constructed as a filter cartridge which has a bed of activated carbon particles between a polyester urethane foam layer and a glass fiber layer.
DE-A 19 816 871 (Sartorius) describes a filtration unit for removing pollutants from fluids.
RU-A 2 027 676 describes a cartridge filter having a sorbent for drinking water purification having a connection to the water tap in the residence.
HU-A 00 209 500 describes a filter cartridge for removing radioactive material and heavy metals from water which is packed with a mixture of ion-exchange material, activated carbon, filter sand, zeolites, aluminum oxide and red mud.
Usually these adsorber cartridges are packed with activated carbon or ion-exchange resins. However, activated carbon has the disadvantage that arsenic salts and heavy metal salts, as they occur in aqueous systems, are not removed to a sufficient extent because of the low adsorption capacity of the activated carbon, and this affects the service life of the cartridges.
This object is achieved by a filtration unit which consists of a housing made of plastic, wood, glass, ceramic, metal or a composite material which is provided with inlet and outlet orifices. Exemplary simple embodiments are described extensively in DE-A 19 816 871. An improved embodiment of an adsorber tank is described in DE-A 10 129 307 or PCT/01/10930. In principle, obviously, other embodiments and designs are possible which resemble the described structures and which operate in the manners described, that is to say comprise an inlet and outlet orifice for waters and iron oxide and/or iron (oxy)hydroxide as adsorber media. The housing space here can be completely or partly filled with the adsorber particles. By packing the housing space with a bed of adsorber particles which takes up between 1 and 99% of the housing volume, a high flow rate of the fluid to be purified is ensured. For, as a result of the stability of the adsorber granules, the influent liquid is opposed by low resistance.
These publications also describe a filter bag which, filled with adsorber granules, can be supplied to a body of water to be purified in order to remove the pollutants present therein by adsorption.
Filter bags and extraction envelopes are known, for example, in many forms and embodiments for preparing hot infused beverages, in particular tea. DE-C 839 405 describes, for example, such a folded bag as used for preparing tea and the like. By means of a special folding technique which forms a double-chamber system, intensive mixing of the eluent with the substance to be extracted is ensured.
The inventive contacts and adsorption media/reaction media, their provision, their use and apparatuses charged with these achieve this complex object. The invention further relates to a process for synthesizing the adsorbers for packing into the inventive filtration units.